Lithologic control on soil texture heterogeneity

Parent material is a soil forming factor which, specially in temperate climates, influences soil hydraulic properties. As direct measurements of the soil hydraulic properties are laborious, time-consuming and expensive, this work explores the influence of geological material on soil hydraulic properties using the Balanced Entropy Index (BEI) as a particle size distribution descriptor which was shown to be useful in the estimation of soil water retention properties. The studied geological materials correspond to the phyllites, quartz-phyllites, metagreywackes, quartzites, schists and granites in the Northern part of Portugal. The source of information used to carry out this study was the soil map of the studied region, scale 1/25,000. Non-parametric Kruskal-Wallis tests, followed by multiple comparisons between pairs of group medians using Bonferroni significant differences (BSD), were applied to determine if soil texture heterogeneity, measured using the BEI, significantly varied between the lithological groups under study. Results clearly show how the type of rock controls the BEI of the overlying soils in the studied area. Further implications of this result are discussed in the text.